/Engine/Plugins/FX/Niagara/Source/Niagara/Classes/NiagaraScript.h
Request an asynchronous compile for the script, possibly forcing it to compile. The output values are the compilation id of the data as well as the async handle to gather up the results with. The function returns whether or not any compiles were actually issued.
bool RequestExternallyManagedAsyncCompile ( const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FNiagaraCompileRequestDataBase](API\Plugins\Niagara\FNiagaraCompileRequestDataBase), ESPMode::ThreadSafe > & RequestData, const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [FNiagaraCompileRequestDuplicateDataBase](API\Plugins\Niagara\FNiagaraCompileRequestDuplicateD-), ESPMode::ThreadSafe > & RequestDuplicateData, [FNiagaraVMExecutableDataId](API\Plugins\Niagara\FNiagaraVMExecutableDataId) & OutCompileId, uint32 & OutAsyncHandle )